This invention relates to clutch cover assemblies of the type (hereinafter called "the type referred to") comprising a cover, a pressure plate axially moveable relatively to said cover, coupling means connecting said cover to said pressure plate which rotates with said cover, resilient means disposed between said cover and said pressure plate and acting axially of said cover whereby said pressure plate is urged in a first axial direction away from said cover towards a first position, the urging force applied to said pressure plate from said resilient means being relievable for allowing movement of said pressure plate in an opposite second axial direction into said cover towards a second position.
Clutch cover assemblies of the type referred to can be used to form clutches wherein a driven plate is clampable between the pressure plate and a rotatably driven driving plate with which the cover is secured fast so as to rotate with the driving plate. In automotive use for example, the driving plate can be rotated by a vehicle engine and may be integral with or connected to a fly-wheel on a crankshaft of the engine.
In known clutch cover assemblies of the type referred to the coupling means can be formed by tangentially disposed leaf-springs forming driving and release straps each attached at one end to the cover and at the other end to the pressure plate. When the urging force applied to the pressure plate from the resilient means is sufficiently relieved, the release straps retract the pressure plate in the second axial direction into the cover to a position corresponding to the clutch being completely disengaged when the cover assembly is in use forming the clutch. Should the release straps be flexed beyond a certain point so as to be over-stressed by an excessive movement by the pressure plate in the first axial direction, this over-stressing impairs their ability to retract the pressure plate. When the clutch cover assembly is not mounted in position to form a clutch, there is a risk of the release straps becoming over-stressed by careless handling such as causing the clutch cover assembly to move swiftly in the first axial direction and then suddenly retarding the cover (as can happen when the cover assembly is dropped to the floor) so that under its own inertia the relatively heavy pressure plate continues moving relatively to cover some further distance in the first direction past the point where the release straps become over-stressed.
Also clutch cover assemblies of the type referred to are known in which the resilient means is acted upon by release levers moved by a release bearing to relieve the urging force provided by the resilient means. For example the resilient means may be a circumferential Belleville portion of a diaphragm spring formed integrally with radially inwardly extending fingers forming the release levers. In the case of cover assemblies for push-type clutches in which the clutch is disengaged by the release bearing pushing on the release fingers in the first axial direction, the envelope or overall space occupied by the cover assembly, prior to connecting with the driving plate, can have an axial length greater than that of the cover due to the release levers being pivoted out through an aperture in a rear of the cover by the resilient means adopting an attitude of minimum stored energy permitted by constraints of the construction of the cover assembly. The axial enlargement of the envelope makes it difficult to fit the cover assembly in a confined space to the driving plate, for example by inserting the cover assembly sideways through a narrow opening in a bell housing of a motor vehicle gearbox. Therefore special service tools have to be provided to retract the pressure plate into the cover so as to act on the resilient means to retract the release levers. Also this retraction of the pressure plate allows the cover assembly to be fitted to the driving plate without being obstructed by the driven plate. In the case of clutch cover assemblies for pull-type clutches in which the clutch is disengaged by the release bearing pulling on the release levers, the resilient means in adopting its position of minimum stored energy may pivot the release levers so far into the cover in the first axial direction towards the pressure plate that they foul against a hub of the driven plate and obstruct the fitting of the cover assembly to the driven plate. To overcome this special service tools may have again to be used to retract the pressure plate into the cover so as to act on the resilient means to swing the release levers in the second axial direction away from the pressure plate In the cases of such pull-and push-type clutches removal of the service tools may be awkward.